I think it's to show that the Volturi KNOW what is going on, and are choosing to ignore it in the hopes of reigning the Cullen's in a bit. That and for the amount of $$ the had to play Dakota I'm sure they wanted her in more than just one scene! ;)

HATE this clip. I don't even care that it doesn't fully fit the book, it just makes me think that I could totally kill the Vulturi with my bare hands an no super powers. They seem LAME not hard ass, scary vampires.